Your Guide to Scan Size vs Print Size
Look, scanning and print size can be confusing. I mean, we’re talking about translating the physical dimensions of a material object into digital measurements that are then used for output into physical dimensions again! What does that even mean?!? Deep breathe, friend. Let’s simplify the relationship between scanning and print size.
Three important terms to understand regarding scan size and print size are “resolution”, “DPI”, and “PPI”. Resolution is the detail an image holds. DPI is a measurement of print resolution meaning “dots per inch”; it’s literally the number of ink dots per inch in a print. Different printers have different resolutions, but 300 DPI is the standard*. The term PPI means “pixels per inch”, and it refers to the digital resolution of an image on a screen.
When the PPI of your digital file is the same as the DPI of your print, it means one image pixel is equal to one ink dot. So, ideally you want your scan to be the same size (in inches and PPI/DPI) or larger than the size you are printing for the clearest image possible (there is some wiggle room here, though it may result in a slightly “softer image”). When you have a smaller digital image than your intended print size, one tiny pixel becomes multiple print dots; the more ink dots used to represent one pixel, the more your image starts to look like a video game from the 1980s.
The image on the left is 300 PPI, where one pixel is equal to one print dot when printed to size. The image on the right is the same image if it was printed at four times the file size, or four dots for every one pixel. Yucky pixilation!
Richard’s standard film scan sizes are small, medium, and large. You can find the approximate pixel dimensions here.
*Fun note: while most printers are around 300 DPI, printers meant for larger work (like billboards or banners) are less than that. Why? Because huge images are meant to be viewed from farther away; while something printed at 150 DPI might look fuzzy and pixilated up close, from a distance it looks like a clear image to your eyes. #scienceystuff